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Counting the Tigers That You Cannot See

a tiger looks into a wildlife camera in India
A tiger investigates a wildlife camera used to document the big cat populations of India. Photograph by Ullas Karanth/WCS.

This is the first in a series of articles on big cat conservation by Ullas Karanth.

Pollsters say tigers are the most popular animal species on this planet. Unfortunately, they are also among the most threatened. Direct killing and overhunting of their prey by humans, as well as habitat reduction by 93% in just two centuries, have all pushed them to the brink. Global efforts are now underway to reverse their decline.

Meanwhile, wildlife biologists like me struggle to monitor the fate of surviving tiger populations. To really know if recovery efforts are working or not, we must count wild tigers. This is not easy: tigers are scarce, secretive and shun human company. History of of tiger counting is littered with failures.

Two young looking tigers walk down a dirt path
Two curious tigers make their way down a dirt path together. Photograph by Ullas Karanth/WCS.

Way back in the 1930s, zoologists tried counting wild tigers across the vast Russian Far East, a region of over 200,000 square kilometers.  Doggedly following fresh tiger tracks in the snow, they tried to distinguish individual cats based on distance between track sets, hoping to get a total count. Although followed to this day, this method has poor statistical basis.

For example, what proportion of tigers are not counted or how many tracks are double-counted, remain unknown. A recent modification, bearing the long-winded name of Formozov–Malyshev–Pereleshin formula, tries to impose statistical discipline. It also, however, involves untestable assumptions. Curiously, around the same time a colonial forester in distant India, J.W. Nicholson, also tried to count tigers by segregating tracks located at waterholes that he thought were sufficiently apart. He also had to make untestable assumptions about how far tigers moved and how often they drank water.

Picture of a tiger walking by a camera trap at night with flash
A large tiger is lit by the flash of a camera trap set in the wilderness. Photograph by Ullas Karanth/WCS.

In the early 1970’s when India launched its ambitious Project Tiger, a senior forestry official—blissfully untrained in either ecology or statistics—proposed an entirely new tiger counting method. He assumed—quite wrongly it turned out—that the paw-print of each individual tiger was uniquely identifiable. Thousands of his Forest Guards fanned out across India—pencil, paper and glass panes in hand—to trace tiger ‘pugmarks’.  They claimed to generate total counts of all tigers in India.

As in Russia, this homegrown and naïve method thrived for decades in an unquestioning bureaucratic culture. In 2005, however, already weakened by tough scientific criticism, the ‘pugmark census’ finally met an inglorious end. It had, quite embarrassingly, failed to detect the poaching of an entire tiger population in Sariska Reserve right next to the rulers in Delhi! A new tiger counting method was desperately sought.

As far back as in 1920s, Indian forester Fred Champion experimented with a cumbersome camera trap developed by William Nesbitt of New York.  Wild animals that walked past tripped it. Illuminated by a magnesium powder flash, Champion’s trap was cumbersome and unreliable: for a lifetime of effort, he got just nine decent tiger photos.  Inspired by Champion, fifty years later, American tiger enthusiast Chuck McDougal used a pressure-pad activated camera trap to obtain some fine tiger portraits in Nepal’s grasslands.

Dr. K Ullas Karanth holds binoculars in a forest as he searches for tiger signs
Dr. K. Ullas Karanth, the director for Science-Asia Wildlife Conservation Society and the Centre for Wildlife Studies, looks for signs of tigers as he works to document the big cats’ population in India. Photograph by Kalyan Varma.

Beginning my tiger studies in the 1980s in the lush Nagarahole forests of India, I focused on understanding tiger population biology rather than getting pretty pictures. I recognized that while the fuzzy paw prints of tigers were unreliable, stripe patterns on their bodies were demonstrably distinct in photographs. However, to estimate a tiger population, I had to deploy dozens of camera traps across vast forests. Expensive and complicated equipment was ruled out.

Fortunately, just at that time, cheap camera traps—used by American deer hunters to identify trophy bucks—came onto the market. In 1990, setting these traps along the favored tiger trails in Nagarahole, I ‘photo-captured’ several distinct tigers, including three that I had radio-collars on. I now had a method that could photograph, identify, and count tigers!

tiger carries animal carcass in its mouth
A camera trap catches a tiger making off with its prey. Photograph by Ullas Karanth/WCS.

However, the next challenge appeared insurmountable. I had to estimate real tiger numbers in order to know how their populations were doing. I needed to answer questions, such as: How many tigers were present each year, how many were born, how many survived, and how many moved in or out.

To understand their population dynamics, in addition to counting tigers I had caught, I had to know how many tigers I had missed. There was no guarantee that every tiger in the population would be caught. Effective conservation demanded real tiger numbers, not just the minimum count from photos. This meant I had to know what proportion of the tiger population I had caught.  In other words, I had to estimate what the chance (probability) that any tiger in the sampled population was photo-captured. To crack this mystery, I had to penetrate a different jungle: one covered in dense thickets of probability statistics, models, and computers.  That is another story.

Comments

  1. moneyman
    benslam
    March 18, 2:59 pm

    i love tigers

  2. Hugh Hunter
    UK
    December 18, 2013, 8:32 am

    I am dismayed at the tone of the comments that imply disrespect for the Indian Gov,nt and forest rangers etc.
    My understanding of this article is that it is about the difficulties of census of Tigers in the wild,not a critique of the Indian methods.
    We should not think it is the Indian intelligence that is disrespected but we should recognise the difficulty of task and the different scientific approach.

  3. Rajendra G Garawad
    Assam, India
    September 5, 2013, 11:49 am

    It appears that Dr Karanth is trying to push through an agenda. While he is quite generous in proclaiming his own achievements, he is highly critical and shows his disdain for the Government of India’s efforts in conserving tiger.

    For example, he writes that “Meanwhile, wildlife biologists like me struggle to monitor the fate of surviving tiger populations. To really know if recovery efforts are working or not, we must count wild tigers.”

    Whose recovery efforts he is referring to? Though he may go around the forests with an expensive binocular in hand looking for tiger signs but finally who protects these surviving tiger populations? For example, in India, which is home to more than 50 % of world’s Royal Bengal Tiger population, the responsibility to protect these tigers vests with State Forest Departments and the Government of India. And I think these agencies / departments are trying their best within the available resources and constraints as it was demonstrated last year during the first stock taking conference of tiger range countries held in New Delhi .

    Whereas he is quick to highlight the case of Sariska but he would not say a word about the success stories like Kaziranga because to talk about these stories would make him acknowledge the importance of rulers /untrained senior forestry officials in conservation. If today tigers in Kaziranga are thriving it is not because of some wildlife biologist struggling to monitor tigers over there but because of several forest officers and innumerable forest guards who sacrificed their personal lives to protect the wildlife of Kaziranga. I am sure there are similar successful conservation stories elsewhere. Therefore, he starts with a familiar story line where things are all dark and gloomy till the saviour arrives on the scene.

    He writes, “Way back in the 1930s, zoologists tried counting wild tigers across the vast Russian Far East, a region of over 200,000 square kilometers.  Doggedly following fresh tiger tracks in the snow, they tried to distinguish individual cats based on distance between track sets, hoping to get a total count. Although followed to this day, this method has poor statistical basis”.

    Please notice how gentle he is on zoologists for practicing a method having poor statistical basis perhaps because those zoologists belongs to his own tribe. It is ok if some zoologists in Russian Far East uses tiger tracks. It is also ok if a colonial forester in distant India had tried to count tigers by segregating tracks located at waterholes. But how dare a senior forestry official, who presumably belongs to the establishment of those rulers in Delhi, can think of a method to count tigers? This is nothing but blasphemy!

    And such an attempt deserves to be scorned with beautifully crafted sentence like “In the early 1970’s when India launched its ambitious Project Tiger, a senior forestry official—blissfully untrained in either ecology or statistics—proposed an entirely new tiger counting method. He assumed—quite wrongly it turned out—that the paw-print of each individual tiger was uniquely identifiable.” and “Thousands of his Forest Guards fanned out across India—pencil, paper and glass panes in hand—to trace tiger ‘pugmarks’”. Somebody appears to have an axe to grind. Even Aristotle, Greek philosopher and polymath, erred by claiming that human males have more teeth than females. I wonder what Dr Karanth would write about Aristotle.

    Whether that blissfully untrained senior forestry official’s assumption about uniqueness of paw-print of each individual tiger was completely wrong as suggested by know-it-all Dr Karanth? Well if you read this article “Dare We Follow the Tiger’s Footsteps?” by Stuart Pimm in Cat Watch, then that untrained senior forestry official may not be all that wrong in his assumption.

    Link is here: http://newswatch.nationalgeographic.com/2013/09/04/107023/

    This is what Stuart Pimm writes about identification of individual tigers based on pugmark,

    “At WildTrack (wildtrack.org) we have developed a rigorous, scientific footprint identification technique (FIT) that can identify individual tigers, and also determine their sex with > 90% accuracy.   It can even identify which foot is represented by the print.

    FIT works like this. A person with a digital camera, or smartphone, takes images of footprints along a trail.  They use a ruler to provide a scale, and a GPS to get a geotag for the image. These trackers need a good eye too, but that’s a natural for foresters and anyone who has grown up in tiger range areas.
    After the images are captured they are processed in JMP data visualisation software from the SAS Institute (jmp.com) and a new statistical model developed by WildTrack will tell if the track belongs to a known animal, or a new animal. Tigers can then be mapped, strategies implemented and anti-poaching patrols deployed.
    By the way, where was Dr Karanth in the early 1970s and why didn’t he propose his methodology at that time to the rulers in Delhi? Perhaps, he was getting trained in ecology, statistics and also in the art of denigrating the forest departments and its officials.

    While I appreciate Dr Karanth’s contribution to tiger monitoring, it would be unfair not to give due credit to all those innumerable forest officials of India who are working hard to protect the remaining forest and wildlife of this country. We can do tons of research but that will never ever replace the most challenging task of protecting the forests & wildlife performed by foresters. There is a huge difference between conducting research on tigers with camera traps and protecting tigers, their habitat from all sorts of threats. While Dr Karanth is busy counting tigers with his binocular & cameras, Forest Departments across India are busy protecting tigers and their habitat. It is not a joke to protect tigers in a country of 1.2 billion people.

    With the introduction of phase IV tiger monitoring program (a peer reviewed methdology) by National Tiger Conservation Authority (NTCA), Government of India, all the tiger reserves of India are expected to monitor tigers and their prey base using camera traps. In fact, with the financial and technical assistance from NTCA and Wildlife Institute of India, many of the tiger reserves of India have already started tiger monitoring on their own except the Karnataka state. It’s different story as to why Karnataka Forest Department is not doing phase IV tiger monitoring on their own.

    In India we have already moved on from pugmark method to camera trapping at tiger reserve level but Dr Karanth seems to be stuck in the past permanently because almost every publication of his makes it a point to criticize the pugmark method and those who had used this method in the past.

  4. Vinod Rishi
    Dehradun
    September 2, 2013, 2:04 am

    The article is full of speculative assertions. For its many untruths it is difficult to take it on its face value.